The present invention relates to a surface-sizing agent for providing inexpensive plain papers capable of being printed with high-quality, blur-free image, and a recording paper comprising such a surface-sizing agent.
Inkjet printers are widely used not only as output means for personal computers, but also as means for printing on media of various materials. Widely used as inks for inkjet printers now are those composed of organic dyes dissolved in water or other solvents, and organic dyes include azo dyes, anthraquinone dyes, indigo dyes, phthalocyanine dyes, carbonium ion dyes, nitro dyes, quinoline dyes, naphthoquinone dyes, etc.
To clearly develop the color of the above inks while preventing the printed ink from blurring, so-called coated papers comprising ink-bearing layers made of high-water-absorption resins on surface, as disclosed by Japanese Patent Laid-Open Nos. 59-35977 and 1-135682, are used for inkjet printers. Such coated papers, however, are high in production cost because of special coatings, and lack in such hand as that of plain papers. In addition, the coated papers produce large amounts of ash when burned, leading to undesirable results in waste treatment. Accordingly, demand is now mounting on commonly usable, inexpensive plain papers suitable for inkjet printers.
When a plain paper is used for an inkjet printer, however, the ink diffuses along fibers of the paper in the course of absorption into the paper, resulting in ink dots with excess blur, and so-called feathering such as irregular peripheries, indistinct outlines, etc. Thus, clear letters and image cannot easily be obtained.
In view of such problems, Japanese Patent Laid-Open Nos. 6-287887 and 6-287888 disclose bacterial cellulose-containing papers produced from a pulp slurry containing fine fibrous cellulose such as bacterial cellulose. However, such inner sizing provides insufficient sizing effects, failing to provide full sizing effects.
Accordingly, an object of the present invention is to provide an inexpensive surface-sizing agent with which plain papers are coated or impregnated to turn them to recording papers capable of providing blur-free, high-quality image while preventing ink dots formed by ink drops from spreading.
Another object of the present invention is to provide a recording paper comprising such a surface-sizing agent.
As a result of intensive research in view of the above objects, the inventors have found that the application of a surface-sizing agent comprising bacterial cellulose and/or plant-originated fine fibrous cellulose (having an average diameter of 10 xcexcm or less) and a cationic polymer to a raw paper provides a recording paper with reduced ink blurring. The present invention has been completed based on this finding.
The recording paper according to the present invention is characterized by being sized with a surface-sizing agent comprising bacterial cellulose and/or plant-originated fine fibrous cellulose (having an average diameter of 10 xcexcm or less) and a cationic polymer.
Fibers of broadleaf tree pulp are generally as wide as about 30 xcexcm. Therefore, when printing is made on plain papers formed from broadleaf tree pulp, an ink blurs along paper fibers, resulting in so-called feathering, namely ink dots with excess blur, irregular peripheries, indistinct outlines, etc. According to the present invention, however, a fine network of fine fibrous cellulose is formed on a surface of a paper by sizing, solving these problems.
Because the surface-sizing agent is coated on a surface of a paper according to the present invention, the fine fibrous cellulose remains in the vicinity of a paper surface. Therefore, even an extremely small amount of fine fibrous cellulose can provide the same effects as those of the conventional internal sizing.
Because the sizing agent of the present invention comprises a cationic polymer, coloring materials contained in an ink are associated with the cationic polymer by ionic interaction near a surface of a recording paper while penetrating into the recording paper, resulting in instantaneous separation from a solution phase, which leads to further improvement in fixing and color development of the ink. The cationic polymer preferably is at least partially bonded to the fine fibrous cellulose. With the cationic polymer fixed to the fine fibrous cellulose, the cationic polymer remains near a paper surface together with the bacterial cellulose, resulting in difficulty in penetrating into the raw paper. Therefore, enough effects can be obtained by a smaller amount of the cationic polymer.